Combining crossStaff with a central beam

[Paul Hodges]

I am trying to set the attached image (both staves are bass clef).  I have written the tuplet (without the note on the top staff in the first chord) in my lower staff voice and jumping between staves as required; the missing note I have set in my top staff voice as the first note of a tuplet with bracket and number hidden and followed by the required skip.  But I can't find any way to make the two parts of the first chord join up, because the \crossStaff directive requires the stems to be in the same direction, and here they are inherently not so.

Any ideas?

I can produce non-working code if required, but I think the description of the problem is enough.

Paul

tuplet.jpg
Description: JPEG image